Re: Servlet

I'm not exactly sure what you mean here?  You can create a custom event 
gateway and extend DefaultEventGateway.  You can also use the 
DefaultEventGateway in the event-gateway.xml file to register your events 
with event handlers.  Here is a simple way to do things....

in web.xml....

     <servlet>
         <servlet-name>ApplicationGateway</servlet-name>
         <servlet-class>org.enhydra.barracuda.core.event.ApplicationGateway</servlet-class>
         <init-param>
             <param-name>ApplicationAssembler</param-name>
             <param-value>org.enhydra.barracuda.core.event.DefaultApplicationAssembler</param-value>
         </init-param>
         <init-param>
             <param-name>AssemblyDescriptor</param-name>
             <param-value>/WEB-INF/event-gateway.xml</param-value>
         </init-param>
         <init-param>
             <param-name>SAXParser</param-name>
             <param-value>org.apache.xerces.parsers.SAXParser</param-value>
         </init-param>
         <load-on-startup>3</load-on-startup>
     </servlet>

in event-gateway.xml...

<?xml version="1.0" encoding="UTF-8" standalone="yes" ?>

<assemble>

         <event-gateway 
class="org.enhydra.barracuda.core.event.DefaultEventGateway">
         <!-- Request event handler for listening for all other request events.
              Does work and then allows the request be handled by the
              originally requested event. -->
         <event-interest 
factory="com.mycompany.myapp.servlet.controller.handler.LocalRequestHandler" 
event="com.mycompany.myapp.servlet.controller.event.LocalRequestEvent" />

         <!-- Individual Request events. These event handlers actually handle
              the request, store info in the event context, and pass
              execution to the render handler below -->
         <event-interest 
factory="com.mycompany.myapp.servlet.controller.handler.GetCatalogHandler" 
event="com.mycompany.myapp.servlet.controller.event.GetCatalog" />
         <event-interest 
factory="com.mycompany.myapp.servlet.controller.handler.GetUserInfoHandler" 
event="com.mycompany.myapp.servlet.controller.event.GetUserInfo" />
         <event-interest 
factory="com.mycompany.myapp.servlet.controller.handler.GetOrdersHandler" 
event="com.mycompany.myapp.servlet.controller.event.GetOrders" />

         <!-- Response Event handler  -->
         <event-interest 
factory="com.mycompany.myapp.servlet.controller.handler.RenderEventHandler" 
event="com.mycompany.myapp.servlet.controller.event.RenderEvent" />
     </event-gateway>

</assemble>


Prototypical event handler (use this as a template for your custom event 
handlers such as GetCatalogHandler, GetUserInfoHandler, and 
GetOrdersHandler)....

package com.mycompany.myapp.servlet.controller.handler;

import java.io.*;
import java.util.*;
import javax.servlet.*;
import javax.servlet.http.*;

import org.enhydra.barracuda.core.event.*;

import com.mycompany.myapp.servlet.controller.event.*;


/**
  * A control event handler
  */
public class PrototypicalEventHandler extends DefaultListenerFactory {

     //define the necessary factory methods
     public BaseEventListener getInstance() {
         return new ControlHandler();
     }
     public String getListenerID() {
         return getID(ControlHandler.class);
     }

     //------------------------------------------------------------
     //             Model 2 - Controller Event Handlers
     //------------------------------------------------------------
     /**
      * handle the request
      */
     class ControlHandler extends DefaultBaseEventListener {
         public void handleControlEvent(ControlEventContext context) throws 
EventException, ServletException, IOException {
             //in this case, we're not really doing anything special, so just
             //redirect to the RenderEvent view
             context.putState(RenderEventHandler.HANDLED_BY, ""+this);
             context.getQueue().addEvent(new RenderEvent(context.getEvent()));
         }
     }
}


Example render handler....

package com.mycompany.myapp.servlet.controller.handler;

import java.io.*;
import java.util.*;
import javax.servlet.*;
import javax.servlet.http.*;

import org.enhydra.barracuda.core.event.*;

import com.mycompany.myapp.servlet.controller.event.*;


/**
  * A view event handler
  */
public class RenderEventHandler extends DefaultListenerFactory {

     private static final Logger logger = 
Logger.getLogger(RenderEventHandler.class.getName());

     //package access only
     static final String HANDLED_BY = "HandledBy";

     //define the necessary factory methods
     public BaseEventListener getInstance() {
         return new ViewHandler();
     }
     public String getListenerID() {
         return getID(ViewHandler.class);
     }

     //------------------------------------------------------------
     //                Model 2 - View Event Handlers
     //------------------------------------------------------------
     /**
      * RenderHandler - handle the request to render the test
      * screen
      */
     class ViewHandler extends DefaultBaseEventListener {
         public void handleViewEvent(ViewEventContext context) throws 
EventException, ServletException, IOException {
             //unpack the necessary entities from the context
             HttpServletResponse resp = context.getResponse();

             //set the caching hdrs (allow this page to be cached by browser)
             resp.setHeader("Cache-Control","max-age=0");
             resp.setDateHeader("Last-Modified", System.currentTimeMillis());

             //build the response
             resp.setContentType("text/html");
             PrintWriter out = resp.getWriter();

             //header
             String title = "Simple Deployment Descriptor Test Screen";
             out.println ("<html>");
             out.println ("  <head>");
             out.println ("    <title>"+title+"</title>");
             out.println ("  </head>");
             out.println ("  <body>");
             out.println ("    <font face=\"Arial\">");

             //body
             out.println ("      <p>"+title);
             out.println ("      <p>Handled by:"+context.getState(HANDLED_BY));

             //footer
             out.println ("    </font>");
             out.println ("  </body>");
             out.println ("</html>");
         }
     }
}


Of course you need to define your events.  Do that using an events.xml file 
and let the <events> taskdef do the work of generating the events...

<?xml version="1.0" encoding="ISO-8859-1"?>
<!DOCTYPE build-events
     PUBLIC "-//Enhydra Barracuda//DTD Barracuda Events 1.0//EN"
     "http://barracuda.enhydra.org/Barracuda/dtds/BarracudaEventBuilder.dtd">

<build-events pkg="com.mycompany.myapp.servlet.controller.event">
     <req-events>
         <event name="LocalRequestEvent">
             <event name="GetCatalog"/>
             <event name="GetUserInfo"/>
             <event name="GetOrders"/>
         </event>
     </req-events>
     <resp-events>
         <event name="LocalResponseEvent">
             <event name="RenderEvent"/>
         </event>
     </resp-events>
</build-events>


That's about it.  Notice that we didn't even code an application or event 
gateway.  We just used the default ones that come with Barracuda.

Hope that helps,

Jake

At 12:02 PM 4/4/2003 -0500, you wrote:
>Are there easy ways to extend these GateWay's? If yes,
>what rules should I follow?
>
>Xue-Feng
>
>  --- Jacob Kjome <[email protected]> wrote: >
> > You can do one of a couple things...even both at the
> > same time...
> >
> > in web.xml...
> >
> >      <servlet>
> >
> > <servlet-name>ApplicationGateway</servlet-name>
> >
> >
><servlet-class>org.enhydra.barracuda.contrib.dbroggisch.examples.controller.DBRApplicationGateway</servlet-class>
> >          <init-param>
> >
> > <param-name>ApplicationAssembler</param-name>
> >
> >
><param-value>org.enhydra.barracuda.core.event.DefaultApplicationAssembler</param-value>
> >          </init-param>
> >          <init-param>
> >
> > <param-name>AssemblyDescriptor</param-name>
> >
> >
><param-value>/WEB-INF/event-gateway.xml</param-value>
> >          </init-param>
> >          <init-param>
> >              <param-name>SAXParser</param-name>
> >
> >
><param-value>org.apache.xerces.parsers.SAXParser</param-value>
> >          </init-param>
> >          <load-on-startup>3</load-on-startup>
> >      </servlet>
> >
> >
> > in DBRApplicationGateway....
> >
> >      public void initializeLocal() {
> >          specifyEventGateways(new
> > RenderPageEventGateway());
> >
> >      }
> >
> >
> > in event-gateway.xml...
> >
> > <?xml version="1.0" encoding="UTF-8"
> > standalone="yes" ?>
> >
> > <assemble>
> >
> > <!-- You can turn on URL rewriting by uncommenting
> > this out
> >      <constant
> >
>class="org.enhydra.barracuda.plankton.http.URLRewriter"
> >
> > name="REWRITE_URLS">true</constant>
> > -->
> >
> >      <event-gateway
> >
>class="org.enhydra.barracuda.core.event.DefaultEventGateway">
> >          <event-gateway
> >
>class="org.enhydra.barracuda.contrib.dbroggisch.examples.controller.ExampleGateway"
> >
> > />
> >      </event-gateway>
> >
> > </assemble>
> >
> >
> > So, we've added both RenderPageEventGateway and
> > ExampleGateway as
> > sub-gateways of the custom DBRApplicationGateway.
> >
> >
> >
> > You can also add subgateways to your event gateways
> > like this...
> >
> > In BarracudaConfig (which is an event gateway)....
> >
> >      public BarracudaConfig() {
> >          ...
> >          ...
> >          ...
> >          //add in sub-gateways
> >          this.add(new CompConfig());
> >          this.add(new DataConfig());
> >          this.add(new DomConfig());
> >          this.add(new EventConfig());
> >          this.add(new FormsConfig());
> >          this.add(new UtilConfig());
> >          this.add(new ViewConfig());
> >          this.add(new MasterConfig());
> >      }
> >
> > or this (in an event-gateway.xml)....
> >
> > <event-gateway
> >
>class="org.enhydra.barracuda.core.event.DefaultEventGateway">
> >          <event-gateway
> > class="com.mypackage.MySubEventGateway1" />
> >          <event-gateway
> > class="com.mypackage.MySubEventGateway2" />
> >          <event-gateway
> > class="com.mypackage.MySubEventGateway3" />
> > </event-gateway>
> >
> >
> > So, you can do everything in application gateway
> > and/or event gateway
> > classes or do everything in the event-gateway.xml
> > file read in by the
> > application assembler.  The advantage of doing the
> > former is compile-time
> > assurance that your application is set up right.
> > The advantage of the
> > former is ease of configuration and the ability to
> > mix and match event
> > gateways and/or event handlers without recompiling
> > anything.
> >
> > Does that help?
> >
> > You might also want to read the 30,000 foot overview
> > and the other docs on
> > the event model:
> > http://barracudamvc.org/Barracuda/index_details.html
> >
> >
> > Jake
> >
> >
> > At 10:11 AM 4/4/2003 -0500, you wrote:
> > >Yes, now I see ApplicationGateway has a method
> > >
> > >public final void add(EventGateway eg)
> > >
> > >Where are the codes that actually 'add' all
> > >'DefaultEventGateway's?
> > >
> > >Maybe I should ask differently.
> > >
> > >Each specific DefaultEventGateway contains main
> > >information of MVC for each page. I just want to
> > >understand the code flow how the servlet treats
> > these
> > >DefaultEventGateway's step by step.
> > >
> > >
> > >Thanks,
> > >
> > >Xue-Feng
> > >
> > >
> > >  --- Jacob Kjome <[email protected]> wrote: >
> > > > Are you wondering about the ApplicationGateway?
> > > > That extends
> > > > HttpServlet.  You add event gateways to the
> > > > application gateway.
> > > >
> > > > Jake
> > > >
> > > > At 07:34 PM 4/3/2003 -0500, you wrote:
> > > > >Hi Jack,
> > > > >
> > > > >I guess that DefaultEventGateway should be
> > comsumed
> > > > by
> > > > >some servlet. Could you please tell me which
> > > > servlet
> > > > >consumes the class which entends
> > > > DefaultEventGateway?
> > > > >Or correct me.
> > > > >
> > > > >Xue-Feng
> > > > >
> > > > >
> > > > >
> > > >
> > >
> >
> >______________________________________________________________________
> > > > >Post your free ad now!
> > http://personals.yahoo.ca
> > > > >_______________________________________________
> > > > >Barracuda mailing list
> > > > >[email protected]
> > > >
> > >http://barracudamvc.org/lists/listinfo/barracuda
> > > >
> > >
> >
> >______________________________________________________________________
> > >Post your free ad now! http://personals.yahoo.ca
> > >_______________________________________________
> > >Barracuda mailing list
> > >[email protected]
> > >http://barracudamvc.org/lists/listinfo/barracuda
> >
>
>______________________________________________________________________
>Post your free ad now! http://personals.yahoo.ca
>_______________________________________________
>Barracuda mailing list
>[email protected]
>http://barracudamvc.org/lists/listinfo/barracuda